The present commercial bitumen extraction process for mined oil sands is Clark hot water extraction technology or its variants that use large amounts of water and generate a great quantity of wet tailings. Part of the wet tailings becomes fluid fine tailings (FFT), which contain approximately 30% fine solids and are a great challenge for tailings treatment. In addition, certain “problem” oil sands, often having high fines content, yield low bitumen recoveries in the water-based extraction process. This leads to economic losses and environmental issues with bitumen in wet tailings.
An alternative to water-based extraction is solvent extraction of bitumen from mined oil sands, which uses little or no water, generates no wet tailings, and can potentially achieve higher bitumen recovery than the existing water-based extraction, especially from the aforementioned problem oil sands. Therefore, solvent extraction is potentially more robust and more environmentally friendly than water-based extraction.
One key challenge of solvent extraction processes is to promote flocculation/agglomeration of oil sand solids with an added bridging liquid (e.g., water) for fast filtration rates while maintaining the total water content in solids low enough for subsequent solids drying and solvent recovery. In general, flocculation requires lower water addition and generates smaller aggregates (flocs or microagglomerates, near 0.2-0.6 mm) causing slower filtration, and agglomeration requires higher water addition and generates larger aggregates (agglomerates, near 1 mm or larger) causing faster filtration. This is because agglomerates generally require more bridging liquid (water) to fill their pores while flocs require less bridging liquid (water). Since most of the added water needs to be boiled off during solids drying and solvent recovery, ideally, it is desirable to generate agglomerates that allow faster filtration but with lower water addition.
Agglomeration of oil sand solids present in hydrocarbons has been discussed in the literature. In solvent extraction spherical agglomeration (SESA) process (U.S. Pat. No. 4,719,008), the water/solids (W/S) mass ratio in extracted (or spent) oil sand is in the range of 0.08-0.15 to generate “agglomerates” of a broad size range of 0.1-2 mm. In its examples (Tables IX and X of U.S. Pat. No. 4,719,008), the W/S ratio is 0.1-0.12 and the “agglomerate” size is around 0.5 mm, which indicates that they were indeed microagglomerates. The apparatus to make the microagglomerates is a horizontal tumbler with rods inside.
In a later process (CA Pat 2740468), microagglomerates of 0.1-1 mm are produced with a broad range of W/S ratio 0.02-0.25. In its example (paragraph [0095] in CA Pat 2740468), the W/S ratio is 0.11, similar to that of SESA process. The apparatus to make these microagglomerates includes all forms of agitation, e.g. mixing tanks, blenders, attrition scrubbers and tumblers. No specifics were given except that the mixing vessels must have a sufficient amount of agitation to keep the formed agglomerates in suspension.
Despite the high W/S ratio of above 0.1, the prior art methods do not appear to generate large agglomerates of near 1 mm or larger, which would be ideal for rapid and economic hydrocarbon drainage.